Re: [RFC] LKMM: Add volatile_if()

[Alexander Monakov]

On Sun, 6 Jun 2021, Linus Torvalds wrote:

> On Sun, Jun 6, 2021 at 11:59 AM Jakub Jelinek <jakub@xxxxxxxxxx> wrote:
> >
> > I think just
> > #define barrier() __asm__ __volatile__("" : : "i" (__COUNTER__) : "memory")
> > should be enough
> 
> Oh, I like that. Much better.
> 
> It avoids all the issues with comments etc, and because it's not using
> __COUNTER__ as a string, it doesn't need the preprocessor games with
> double expansion either.
> 
> So yeah, that seems like a nice solution to the issue, and should make
> the barriers all unique to the compiler.

It also plants a nice LTO time-bomb (__COUNTER__ values will be unique
only within each LTO input unit, not across all of them).

Alexander